用火柴棒按图的方法搭三角形：

按图示的规律搭下去，则所用火柴棒数a_n 与所搭三角形的个数n之间的关系式可以是____．

 根据对话内容，用方框中所给单词的适当形式填空，每词限用一次。

water    no    Earth    it    for

Bill: I saw a great programme on TV about space yesterday evening.
Tony: What is ____ about?  
Bill: Scientists have discovered ____ on Mars.
Tony: Really? That's very fantastic. Have they discovered life on Mars?
Bill: Well, they're looking____  life but they haven’t found anything yet.
Tony: I know there's ____ life on the moon.
Bill: Yes, that's right. So far there's only life on ____ .
Tony: Are we alone with so many stars in the universe?
Bill: I am interested in it, so I want to be a scientist when I grow up.
Tony: I wish you will.

综合题。

我们身边有许多应用杠杆的实例，以下一定属于省力杠杆的是（   ）

《最后一次讲演》是____在____的追悼会上所作的演讲。